Method of improving the acrylic rubber sealant compatibility in an internal combustion engine

ABSTRACT

It has been discovered that a lubricating oil composition containing a certain combination of a nitrogen-containing dispersant and a metal-containing detergent of an alkali metal salt of alkylphenol derivative having a Mannich base structure, together with a phosphorus-containing organic compound, can be effectively employed in a method for improving the acrylic rubber sealant compatibility in an internal combustion engine, if the ratio of the nitrogen-containing dispersant and a metal-containing detergent of an alkali metal salt of alkylphenol derivative having a Mannich base structure is adjusted to a specific range, i.e., in the range of from 1:0.005 to 1:2 in terms of the nitrogen contents.

The present invention relates to a method of improving the acrylicrubber sealant compatibility in an internal combustion engine. Morespecifically, the present invention relates to a method comprisingcontacting acrylic rubber sealants in an internal combustion engine andoperating the internal combustion engine with a lubricating oilcomposition having improved acrylic rubber sealant compatibility.

BACKGROUND OF THE INVENTION

In mechanical devices such as internal-combustion engine vehicles andvarious other industrial machines, it is necessary to supply alubricating oil to mechanisms involving rubbing movement. Lubricationsystems for supplying a lubricating oil are generally equipped withvarious sealing materials (sealants). Examples of the sealing materialsinclude resin or rubber sealants such as silicone rubber sealant,acrylic rubber sealant, fluorocarbon resin sealant, nitrile rubbersealant, hydrogenated nitrile rubber sealant and ethylene-propylenerubber sealant. According to their physical and chemicalcharacteristics, those sealants are optionally selected to be installedin proper parts of the lubrication systems. Among the above-mentionedmaterials, acrylic rubber sealant is particularly used as packing partsfor fixation because it is not only excellent in heat resistance and oilresistance but also inexpensive,

At the present time, it is required to improve lubricating oils for thepurpose of meeting certain performance requirements. Most lubricatingoils contacting rubbing mechanisms in various machines are nowadayhigh-performance lubricating oil compositions comprising a lubricatingbase oil and various additives added thereto.

However, lubricating oil compositions containing various additives oftendeteriorate resin or rubber sealants despite satisfying lubricatingperformance requirements. Most of the additives contained in thecompositions are so chemically active that they are liable to shrink thesealants and/or to impair their strength and elasticity.

Accordingly, it is desirable to have a lubricating oil composition whichsatisfies the severe performance requirements concerning lubricating oilcompositions and, at the same time, which hardly impairs sealingperformance of the sealants themselves.

U.S. Pat. No. 6,124,247 describes a lubricating oil compositioncontaining a borated glycerol ester and a mono-succinimide orbis-succinimide type dispersant subjected or not subjected topost-treatment with, for example, ethylene carbonate. It is stated thatthis oil composition has excellent compatibility with fluorocarbonelastomer, which is used as a sealant in a lubrication system of aninternal-combustion engine.

JP-A-11-181461 describes that a lubricating oil composition containingan aliphatic amine has excellent compatibility with rubber sealants.

U.S. Pat. No. 6,569,818 describes a lubricating oil compositioncontaining an ashless dispersant of an alkenyl- or alkyl-succinic imideor a derivative thereof, an alkali metal or alkaline earth metalalkylsalicylate of non-sulfide or otherwise an alkali metal salt ofalkylphenol derivative having a Mannich base structures a zincdialkyldithiophosphate, and an oxidation inhibiting phenol or aminecompound. It is stated that all of the ash content, the phosphoruscontent and the sulfur content of the disclosed lubricating oilcomposition are low levels and that the lubricating oil compositiongives high detergency at a high temperature. U.S. Pat. No. 6,569,818,however, is silent about a lubricating oil composition of the presentinvention described hereinbelow. Further, this reference neitherdescribes nor suggests any effect that the lubricating oil compositionhas on sealants.

SUMMARY OF THE INVENTION

The present invention relates to a method of improving acrylic rubbersealant compatibility in an internal combustion engine. The methodinvolves contacting the acrylic rubber sealant in the internalcombustion engine and operating the internal combustion engine with alubricating oil composition comprising:

-   -   a) a major amount of a base oil of lubricating viscosity,    -   b) a nitrogen-containing ashless dispersant in an amount of 0.01        to 0.3 wt. %, preferably 0.01 to 0.1 wt. %, in terms of the        nitrogen content based on the total amount of the lubricating        oil composition,    -   c) a metal-containing detergent of an alkali metal or alkaline        earth metal salt of alkylphenol derivative having a Mannich base        structure in an amount of 0.001 to 0.4 wt. % in terms of the        metal content or 0.002 to 0.1 wt. % in terms of the nitrogen        content, based on the total amount of the lubricating oil        composition, and    -   d) a phosphorus-containing organic compound in an amount of        0.001 to 0.5 wt. %, preferably 0.01 to 0.2 wt. %, in terms of        the phosphorus content, based on the total amount of the        lubricating oil compositions    -   wherein the ratio of components b) to c) is in the range of from        1:0.005 to 1:2, preferably 1:0.01 to 1:0.3, in terms of the        nitrogen content.

The nitrogen-containing ashless dispersant in the lubricating oilcomposition employed in the method of the present invention is analkenyl- or alkyl-succinic imide or a derivative thereof.

The metal-containing detergent of an alkali metal or alkaline earthmetal salt of alkylphenol derivative in the lubricating oil compositionemployed in the method of the present invention has a Mannich basestructure represented by the following formula:

wherein R is an alkyl group having 8 to 30 carbon atoms, and n is 0 or apositive integer.

The lubricating oil composition employed in the method of the presentinvention may further comprise a phosphorus-containing organic compoundselected from the group consisting of zincdihydrocarbyldithiophosphates, zinc dihydrocarbylphosphates, phosphoricacid esters, phosphorous acid esters, and thiophosphoric acid esters.

The lubricating oil composition employed in the method of the presentinvention may further comprise a metal-containing detergent selectedfrom the group consisting of alkali metal or alkaline earth metalsalicylates, carboxylates, phenates and sulfonates in an amount of 1.0wt. % or less in terms of the metal content.

The amount of metal-containing detergent selected from the groupconsisting of alkali metal or alkaline earth metal salicylates,carboxylates, phenates and sulfonates to the amount of metal-containingdetergent of an alkali metal or alkaline earth metal salt of alkylphenolderivative having a Mannich base structure is in a ratio of 1:0.003 to1:1 in terms of the metal content.

The lubricating oil composition employed in the method of the presentinventions may further comprise a molybdenum compound selected from thegroup consisting of an oxymolybdenum complex prepared by the reactionbetween an acidic molybdenum compound and a basic nitrogen compoundssulfurized oxymolybdenum dithiocarbamate, and sulfurized oxymolybdenumdithiophosphate, in amount of 0.25 wt. % or less in terms of themolybdenum content.

The lubricating oil composition employed in the method of the presentinvention may further comprise an alkali metal borate in an amount of 2wt. % or less and an oxidation inhibitor selected from the groupconsisting of hindered phenol compounds and diarylamine compounds in anamount of 5 wt. % or less.

The base oil of lubricating viscosity contains 10 wt. % or more of amineral oil showing the following characteristics:

-   -   17 wt. % or less evaporation loss according to ASTM: D-5800,    -   90 wt. % or more saturated content,    -   10 wt. % or less, aromatic component,    -   0.01 wt. % or less, sulfur content, and    -   120 or more viscosity index.

The lubricating oil composition employed in the method of the presentinvention is a SAE viscosity grade selected from the group consisting of0W20, 0W30, 5W20, 5w30 and 10W30. Preferably, the lubricating oilcomposition meets the SAE 10W-30 viscosity grade.

Among other aspects, it has been discovered that a lubricating oilcomposition containing a certain combination of a nitrogen-containingdispersant and a metal-containing detergent of an alkali metal salt ofalkylphenol derivative having a Mannich base structure, together with aphosphorus-containing organic compound, can be effectively employed in amethod for improving the acrylic rubber sealant compatibility in aninternal combustion engine, if the ratio of the nitrogen-containingdispersant and a metal-containing detergent of an alkali metal salt ofalkylphenol derivative having a Mannich base structure is adjusted to aspecific range, i.e., in the range of from 1:0.005 to 1:2 in terms ofthe nitrogen content. The lubricating oil composition hardly impairs thesealing performance of the acrylic rubber sealant.

DETAILED DESCRIPTION OF THE INVENTION

The present invention resides in a method of employing a certainlubricating oil composition to improve the acrylic rubber sealantcompatibility in an internal combustion engine. The lubricating oilcomposition, while meeting the lubricating performance requirements ofinternal combustion engines, at the same time is less detrimental to thesealing performance of acrylic rubber sealants found in internalcombustion engines as compared to conventionally used lubricating oilcompositions. Thus, the method of the present invention advantageouslyimproves the acrylic rubber sealant compatibility in internal combustionengines.

The preferred embodiments of the present invention will be described infurther detail below. It should be noted that when weight percent isused. herein, it is based on the total weight percent of the lubricatingoil composition unless otherwise specified.

The lubricating oil composition employed in the method of the presentinvention will contain a nitrogen-containing ashless dispersant. Thenitrogen-containing ashless dispersant is preferably is apolyolefin-derived alkenyl- or alkyl-succinic imide or a derivativethereof. The amount of the nitrogen-containing ashless dispersant is inthe range of 0.01 to 0.3 w.% preferably 0.01 to 0.1 wt. %, in terms ofthe nitrogen content, based on the total amount of the lubricating oilcomposition.

A representative succinic imide can be prepared by the reaction betweensuccinic anhydride having a high molecular weight alkenyl or alkylsubstituent group with polyalkylenepolyamine containing 4 to 10 nitrogenatoms on average, preferably 5 to 70 nitrogen atoms. The high molecularweight alkenyl or alkyl substituent group is preferably a polybutenehaving a number average molecular weight of approximately 900 to 5,000.

The process for preparing the polybutenylsuccinic anhydride by thereaction between polybutene and maleic anhydride is generally performedby a chlorination method utilizing chlorine. While this reaction isadvantageous in giving a high reaction yield, it has a disadvantageousfeature in that a large amount (for instance, approximately 20,000 to3,000 ppm) of chlorine remains in the final succinic imide product. Incontrast, a thermal reaction process utilizing no chlorine can give afinal reaction product having an extremely low chlorine content (such as0 to 30 ppm). It is, therefore, preferred to use a succinic imidederived from the polybutenylsuccinic anhydride prepared by the thermalreaction process so that the chlorine content can be in the range of 0to 30 ppm. The resulting succinic imide can be further converted into amodified succinic imide by a further reaction with boric acid, alcohol,aldehyde, ketone, alkylphenol, cyclic carbonate or organic acids. Fromthe thermal stability and oxidation stability particularly preferred isa boron-containing alkenyl- or alkyl-succinic imide which is produced bythe reaction with boric acid or a boron-containing compound.

The lubricating oil composition employed in the method of the presentinvention indispensably contains the ashless dispersant, whoserepresentative example is an alkenyl- or alkyl-succinic imide or aderivative thereof. As the ashless dispersant, ashless dispersants ofalkenylbenzylamine type and alkenylsuccinic acid ester type can be alsoused,

The lubricating oil composition employed in the method of the presentinvention will contain metal-containing detergent of an alkali metal oralkaline metal earth metal salt of alkylphenol derivative. Themetal-containing detergent of an alkali metal or alkaline metal earthmetal salt of alkylphenol derivative has a Mannich base structurerepresented by the following formula,

The amount of the metal-containing detergent of an alkali metal oralkaline earthmetal salt of alkylphenol derivative having a Mannich basestructure is in the range of 0.001 to 0.4 wt. % in terms of the metalcontent or 0,002 to 0.1 wt. % in terms of the nitrogen content, based onthe total amount of the lubricating oil composition.

The metal-containing detergent of an alkali metal (e.g., sodium,potassium) or alkaline earth metal (e.g. calcium, barium, magnesium)salt of alkylphenol derivative having a Mannich base structure, isgenerally prepared by the steps of: synthesizing an intermediate havingaminomethylated phenol ring by Mannich reaction from alkylphenol,formaldehyde, amine or an amine compound; and neutralizing thesynthesized intermediate with a base such as calcium hydroxide to covertit into a metal salt. Examples include the compound of the above formulahaving the following characteristics:

-   -   Ca content: 2.5 wt. %,    -   N content: 1.6 wt. %,    -   total base number: 135 mg·KOH/g, and    -   base number attributable to basic nitrogen: approximately 50% of        the total base number.

The ratio of the nitrogen-containing ashless dispersant to themetal-containing detergent of an alkali metal or alkaline earth metalsalt of alkylphenol derivative having a Mannich base structure is in therange of from 1:0.005 to 1:2, preferably 1:0.01 to 1:0.3 in terms of thenitrogen content.

The lubricating oil composition employed in the method of the presentinvention will contain a phosphorus-containing organic compound selectedfrom the group consisting of zinc dihydrocarbyldithiophosphates, zincdihydrocarbylphosphates, phosphoric acid esters, phosphorous acidesters, and thiophosphoric acid esters. The amount of thephosphorus-containing organic compound is in the range of 0.001 to 0.5wt. %, preferably 0.01 to 0.2 wt. %, in terms of the phosphorus content,based on the total amount of the lubricating oil composition.

Examples of the phosphorus-containing organic compounds include zincdihydrocarbyldithiophosphates, zinc dihydrocarbylphosphates, phosphoricacid esters, phosphorous acid esters, and thiophosphoric acid esters inwhich each ester is generally derived from the corresponding acid and analkylalcohol having 3 to 18 carbon atoms or an alkylaryalcohol having analkyl group of 3 to 18 carbon atoms. If a zincdihydrocarbyldithiophosphate (zinc dialkyldithiophosphate) is added, theamount of the additive is preferably in the range of 0.01 to 0.1 wt. %in terms of the phosphorus content, based on the total amount of thelubricating oil composition. From the viewpoint of reducing thephosphorus content and the sulfur content, the amount preferably is inthe range of 0.01 to 0.06 wt. %, based on the total amount of thelubricating oil composition,

The zinc dialkyldithiophosphate preferably has an alkyl group of 3 to 18carbon atoms or an alkylaryl group having an alkyl group of 3 to 18carbon atoms. It is particularly preferred for the zincdialkyldithiophosphate to have an alkyl group derived from a secondaryalcohol having 3 to 18 carbon atoms or an alkyl group derived from amixture of a primary alcohol having 3 to 18 carbon atoms and a secondaryalcohol having 3 to 18 carbon atoms, because the zincdialkyldithiophosphate having that alkyl group is particularly effectivein wear reduction. A zinc dialkyldithiophosphate derived from a primaryalcohol is also excellent in heat resistance. The zinc dithiophosphatescan be used singly, but it is preferred to use a mixture mainlycomprising a secondary alkyl-type and/or a primary alkyl type

The lubricating oil composition employed in the method of the presentinvention may further contain another metal-containing detergentselected from the group consisting of alkali metal or alkaline earthmetal salicylates, carboxylates, phenates and sulfonates in an amount of1.0 wt. % or less in terms of the metal content, based on the totalamount of the lubricating oil composition.

The amount of the metal-containing detergent selected from the groupconsisting of alkali metal or alkaline earth metal salicylates,carboxylates, phenates and sulfonates to the amount of themetal-containing detergent of an alkali metal or alkaline earth metalsalt of alkylphenol derivative having a Mannich base structure is in aratio of 1:0.003 to 1:1 in terms of the metal content, based on thetotal amount of the lubricating oil composition.

The lubricating oil composition employed in the method of the presentinvention may further contain an oxidation inhibitor selected from thegroup consisting of hindered phenol compounds and diarylamine compoundsin an amount of 5 wt. % or less, based on the total amount of thelubricating oil composition. In view of having a base numberattributable to nitrogen, diarylamine-type oxidation inhibitors areparticularly advantageous. On the other hand, however, hinderedphenol-type oxidation inhibitors effectively prevent deteriorationcaused by NO_(x) oxidation.

Examples of the hindered phenol oxidation inhibitors include2,6-di-t-butyl-p-cresol, 4,4′-methylenebis(2,6-di-t-butylphenol),4,4′-methylenebis(6t-butyl-o-cresol),4,4′-isopropylidenebis(2,6-di-t-butylphenol),4,4′-bis(2,6-di-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylphenol),4,,4′-thiobis(2-methyl-6-t-butylphenol),2,2-thiodiethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],octyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and octadecyl3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,

Examples of the diarylamine oxidation inhibitors include analkyldiphenylamine containing a mixture of alkyl groups having 4 to 9carbon atoms, p,p′-dioctyldiphenylamine, phenyl-α-naphthylamine,phenyl-α-naphthylamine, alkylated α-naphthylamine, and alkylatedphenyl-α-naphthylamine,

Each of the hindered phenol compounds and the diarylamine compounds canbe used singly or in combination. Other oil soluble oxidation inhibitorscan be employed in combination.

The lubricating oil composition employed in the method of the presentinvention may further contain a molybdenum compound selected from thegroup consisting of an oxymolybdenum complex prepared by the reactionbetween an acidic molybdenum compound and a basic nitrogen compound,sulfurized oxymolybdenum dithiocarbamate), and sulfurized oxymolybdenumdithiophosphate, in an amount of 0.25 wt. % or less in terms of themolybdenum content, based on the total amount of the lubricating oilcomposition.

The molybdenum-containing compound mainly functions as a frictionmodifier, an oxidation inhibitor or an anti-wear agent in thelubricating oil composition employed in the method of the presentinvention. In addition, it also improves detergency at a hightemperature. The molybdenum-containing compound is preferably in anamount of 10 to 2,500 ppm in terms of the molybdenum content. Examplesof the molybdenum-containing compounds include sulfur-containingmolybdenum complex of succinimide, sulfurized oxymolybdenumdithiocarbamate, sulfurized oxymolybdenum dithiophosphate, aminemolybdenum complex compound, oxymolybdenum diethylate amide, andoxymolybdenum monoglyceride. Sulfur-containing molybdenum complex ofsuccinimide is particularly effective in improving the detergency at ahigh temperature.

The lubricating oil composition employed in the method of the presentinvention may further contain an alkali metal borate in an amount of 2wt. % or less, based on the total amount of the lubricating oilcomposition. The alkali metal borate hydrate is also effective inimproving the detergency at a high temperature and in giving a basenumber. The term “alkali metal borate hydrate” in the present inventionmeans a compound representatively prepared by the method disclosed inU.S. Pat. Nos. 3,929,650 and 4,089 790. For example, it can be obtainedby the steps of carbonating a neutral alkali metal or alkaline earthmetal sulfonate in the presence of an alkali metal hydroxide to preparea basic sulfonate; and making the basic sulfonate to react with boricacid, to prepare an alkali metal borate in the form of dispersed fineparticles. The carbonation reaction is preferably conducted further inthe presence of an ashless dispersant such as succinic imide. The alkalimetal preferably is potassium or sodium. An example of the alkali metalborate hydrate additive is a suspension comprising a mixture of neutralcalcium sulfonate and succinic imide and fine particles of KB₃O₅.H₂Ohaving sizes of approximately 0.3 μm or less. The potassium can bereplaced with sodium. The additive is also preferably used inconsideration of water resistance.

The lubricating oil composition employed in the method of the presentinvention may further contain a viscosity index improver in an amount of20 wt. % or less, preferably 1 to 20 wt. %, based on the total amount ofthe lubricating oil composition. Examples of the viscosity indeximprover include polymer compounds such as polyalkyl methacrylate,ethylene-propylene copolymer, styrene-butadiene copolymer, andpolyisoprene. Also employable are dispersant-type viscosity indeximprovers, which can be obtained by modifying the above polymers so thatthey can function as dispersants, and multi-functional viscosity indeximprovers. The viscosity index improvers can be used singly or incombination.

The lubricating oil composition employed in the method of the presentinvention may further contain various other auxiliary additives.Examples of the auxiliary additives include zinc dithiocarbamate,methylenebis(dibutyldithiocarbamate), an oil-soluble copper compound, asulfur-containing compound (e.g., sulfurized olefin, sulfurized ester,polysulfide), and an organic amide compound (e.g., oleyl amide). Theyfunction as oxidation inhibitors or anti-wear agents. It is alsopreferred to incorporate metal deactivators such as benzotriazolecompounds and thiadiazole compounds. Further, a nonionic surface activeagent of polyoxyalkylene such as a copolymer ofpolyoxyethylenealkylphenyl ether, ethylene oxide and propylene oxide canbe added as a rust preventing agent or an demulsifier. It is alsopossible to incorporate various amines, amides, amine salts orderivatives thereof, and aliphatic acid esters of polyhydric alcohols ortheir derivatives. They serve as friction modifiers. It is furtherpossible to incorporate various compounds that function as defoamingagents or pour point depressants. Each auxiliary additive is added tothe lubricating oil composition employed in the method of the presentinvention preferably in an amount of 3 wt. % or less, preferably 0.001to 3 wt. %, based on the total amount of the lubricating oilcomposition.

Base Oil of Lubricating Viscosity

The base oil used in the lubricating oil composition employed in themethod of the present invention generally is a mineral or synthetic oilshowing a kinematic viscosity of 2 to 50 mm²/s at 100° C. There are nospecific conditions with respect to the mineral or synthetic oil, butthe base oil has a sulfur content of preferably 0.1 wt. % or less, morepreferably 0.03 wt. % or less, most preferably 0.005 wt % or less.

The mineral base oil is preferably subjected to properly combinedtreatments. For example, the mineral lubricant distillate thereof ispreferably subjected to treatments such as solvent refining andhydrogenation processing in combination. In the present invention, it ispreferred to use a highly hydrogen-refined (hydrocracked) base oil(having, for example, a viscosity index of 100 to 150, an aromaticcomponent content of 5 wt. % or less, a nitrogen content of 50 ppm orless, and a sulfur content of 50 ppm or less). Examples include a highviscosity index-base oil prepared by isomerization or hydrocracking ofsynthetic wax synthesized from slack wax (crude wax) of mineral oil ornatural gas,

It is particularly preferred that the base oil of lubricating viscosityis a mineral oil showing the following characteristics:

-   -   evaporation loss (ASTIM D-5800): 17 wt. % or less,    -   content of saturated component: 90 wt. % or more,    -   content of aromatic component: 10 wt. % or less,    -   sulfur content: 0.01 wt. % or less, and    -   viscosity index: 120 or more,        or otherwise that the base oil of lubricating viscosity is a        mineral oil mixture containing 10 wt. % or more of the        above-mentioned mineral oil.

Examples of the synthetic oils (synthetic lubricant base oil) include apoly-α-olefin (copolymer of α-olefin having 3 to 12 carbon atoms), adialkyl diester (ester derived from an alcohol having 4 to 18 carbonatoms and a dibasic acid such as adipic acid, azelaic acid or sebacicacid) such as dioctyl sebacate, a polyol ester (ester derived from amonobasic acid having 3 to 18 carbon atoms and 1-trimethylolpropane orpentaerythritol), and an alkylbenzene having an alkyl group of 9 to 40carbon atoms.

Any of the above mineral or synthetic base oils may be used singly, buttwo or more of the mineral base oils or two or more of the syntheticbase oils can be used in combination, if desired. Further, the mineraland synthetic base oils can be used in combination at any ratios, ifdesired, to prepare the appropriate base oil of lubricating viscosity.

It is preferred to use a major amount of base oil of lubricatingviscosity in the lubricating oil composition employed in the method ofthe present invention. A major amount of base oil of lubricatingviscosity as defined herein comprises 40 wt % or more. Preferred amountsof base oil comprise 40 to 99.9 wt preferably greater than 50 to 97 wt%, more preferably 60 to 97 wt % of the lubricating oil composition.

The lubricating oil composition employed in the method of the presentinvention can be prepared by adding the additives independently or allat once to the base oil. Otherwise, an additive concentrate comprisingthe additives in high concentrations can be beforehand prepared and thenmixed it with a base oil to prepare the lubricating oil compositionemployed in the method of the present invention.

EXAMPLES

The base oil of lubricating viscosity and the additives used in thebelow-described Examples and Comparative Example are as follows:

(1) Base Oil of Lubricating Viscosity

Solvent refined base oil (A) (kinematic viscosity: 4.9 mm²/s at 100° C.,viscosity index: 103, evaporation loss (ASTM D5800): 13 wt. %, sulfurcontent: 0.19 wt. %, content of saturated component: 70 wt. %) andsolvent refined base oil (B) (kinematic viscosity: 10.8 mm²/s at 100°C., viscosity index: 97, evaporation loss (ASTM D5800): 2.3 wt. %,sulfur content. 0.22 wt. %, content of saturated component: 68 wt. %)were mixed in the ratio of 88:12 by weight to use.

(2) Additives

Dispersant A: ethylene carbonate-treated succinimide dispersant [Ncontent: 1.0 wt. % Cl content: 30 ppm by weight] which was prepared bythe steps of:

-   -   a) reacting a polybutene having a number average molecular        weight of approximately 2,300 and 50% or more of        methylvinylidene structure with maleic anhydride according to        the thermal process, to produce an intermediate product;    -   b) reacting the intermediate product with a        polyalkylenepolyamine containing 6.5 nitrogen atoms (in one        molecule) on average, to prepare succinimide of bis-form; and        then    -   c) treating the succinimide of bis-form with ethylene carbonate.

Dispersant B: boron-containing succinimide dispersant [N content, 1.95wt. %, B content: 0.66 wt. %, Cl content: less than 5 ppm by weight]which was prepared by the steps of

-   -   a) reacting a polybutene having a number average molecular        weight: of approximately 1,300 and 50% or more of        methylvinylidene structure) with maleic anhydride according to        the thermal process, to produce an intermediate product,    -   b) reacting the intermediate product with a        polyalkylenepolyamine containing 6.5 nitrogen atoms (in one        molecule) on average, to prepare succinimide of bis-form; and        then    -   c) treating the succinimide of bis-form with boric acid.

Detergent A: Mannich base calcium phenate (Ca: 2.5 wt. %, N; 1.6 wt. %.S: 0.1 wt. %, TBN: 135 mg·KOH/g),

Detergent B: overbased sulfurized calcium phenate (Ca: 9.25 wt. %, S:3.4 wt. %, TBN: 265 mg·KOH/g).

Detergent C: overbased calcium sulfonate (Ca: 16.1 wt. %, TBN: 425mg·KOH/g).

Detergent D. basic calcium sulfonate (Ca: 2.35 wt. %, TBN: 17 mg·KOH/g).

ZnDTP-1; zinc dialkyldithiophosphate (P: 7.2 wt. %, Zn: 7.85 wt. %, S;14.4 wt. %, starting material; a secondary alcohol having 3 to 6 carbonatoms).

ZnDTP-2; zinc dialkyldithiophosphate (P: 7.3 wt. %, Zn: 8.4 wt. %, S: 14wt. %, starting material; a primary alcohol having 8 carbon atoms).

Oxidation inhibitor; dialkyldiphenylamine (alkyl group: mixture ofC₄-alkyl and C₈-alkyl groups, N: 4.6 wt. %, TBN; 180 mg·KOH/g).

Mo compound: sulfur-containing molybdenum-succinimide complex (Mo: 5.5wt. %, S: 0.2 wt. %, N: 1.6 wt. %, TBN: 10 mg·KOH/g).

Alkali metal borate; dispersed fine particles of potassium boratehydrate (K: 8.3 wt. %, B: 6.8 wt. %, S: 0.26 wt. %, TBN: 125 mg·KOH/g).

Viscosity index improver (VII): ethylenepropylene copolymer ofnon-dispersant type.

Pour point depressant (PPD): polymethacrylic compound.

Example 1

The below-mentioned additives and the base oil of lubricating viscositywere mixed to give: the lubricating oil composition employed in themethod of the present invention. The lubricating oil composition was SAEviscosity grade 10W30. Also shown below are the contents of each element(Ca, P, N) in the lubricating oil composition, the ratio between thenitrogen content attributable to all the dispersants and thatattributable to the detergent A (Mannich base calcium phenate), and theratio between the metal content attributable to all the detergents andthat attributable to the detergent A (Mannich base calcium phenate).

-   (1) Additives    -   Dispersant A (amount: 3.0 wt. %, content in terms of nitrogen:        0.03 wt. %),    -   Dispersant B (amount. 1.5 wt. %, content in terms of nitrogen:        0.03 wt. %),    -   Detergent A (amount: 0.4 wt. %, content in terms of calcium:        0.01 wt. %, content in terms of nitrogen; 0.006 wt. %),    -   Detergent B (amount: 0.86 wt. %, content in terms of calcium:        0.08 wt. %),    -   Detergent C (amount: 0.87 wt., content in terms of calcium: 0.14        wt. %),    -   Detergent D (amount: 0.43 wt. % content in terms of calcium:        0.01 wt. %),    -   ZnDTP-1 (amount: 0.97 wt. %, content in terms of phosphorus:        0.07 wt. %),    -   ZnDTP-2 (amount 0.41 wt. %, content in terms of phosphorus: 0.03        wt. %),    -   Oxidation inhibitor (amount, 0.2 wt. %),    -   Mo compound (amount: 0.15 wt. %, content in terms of molybdenum:        83 ppm by weight),    -   Alkali metal borate (amount: 0.25 wt. %),    -   Viscosity index improver (VII, amount: 6.3 wt. %), and    -   Pour point depressant (PPD, amount: 0.3 wt. %).-   (2) Base oil of lubricating viscosity (amount: residual amount)-   (3) Content of each element (Ca, P, N!) in the lubricating oil    composition    -   Calcium (Ca): 0.24 wt. %, Phosphorus (:P): 0.10 wt. %, Nitrogen        (N): 0.08 wt. %-   (4) Ratio of the nitrogen content attributable to all the    dispersants to that attributable to the detergent A (Mannich base    calcium phenate); 1:0.1-   (5) Ratio of the metal content attributable to all the detergents in    the composition to that attributable to the detergent A (Mannich    base calcium phenate): 1:0.04

Example 2

The procedures of Example 1 were repeated except for changing the amountof the detergent A (Mannich base calcium phenate) into 1.16 wt. %(content in terms of calcium: 0.03wt. %, content in terms of nitrogen:0.018 wt. %) and for changing the residual amount of the base oil oflubricating viscosity so that the total amount of the lubricating oilcomposition is 100 wt. %. The prepared lubricating oil composition wasSAE viscosity grade 10W30. Shown below are the contents of each element(Can P, N) in the lubricating oil composition, a ratio between thenitrogen content attributable to all the dispersants and thatattributable to the detergent A (Mannich base calcium phenate), and aratio between the metal content attributable to all the detergents andthat attributable to the detergent A (Mannich base calcium phenate).

-   (1) Contents of each element (Ca, P, N) in the lubricating oil    composition    -   Calcium (Ca): 0.26 wt. %, Phosphorus (P); 0.10 wt. %, Nitrogen        (N): 0.09 wt. %-   (2) Ratio of the nitrogen content attributable to all the    dispersants to that attributable to the detergent A (Mannich base    calcium phenate): 1:0.3-   (3) Ratio of the metal content attributable to all the detergents in    the lubricating oil composition to that attributable to the    detergent A (Mannich base calcium phenate): 1:0.12

Comparative Example A

Comparative Example A was prepared according to the procedures ofExample 1 except for not adding the detergent A (Mannich base calciumphenate) and for changing the amount of the base oil of lubricatingviscosity so that the total amount of the lubricating oil composition is100 wt. %. The prepared lubricating oil composition was SAE viscositygrade 10W30. The contents of each element (Ca, P, N) in the lubricatingoil composition are shown below.

-   (1 ) Contents of each element (Ca, P, N) in the lubricating oil    composition    -   Calcium (Ca): 0.23 wt. %, Phosphorus (P): 0.10 wt. %, Nitrogen        (N): 0.07

Evaluation of Compatibility with Acrylic Rubber Sealant

According to the affinity test for sealing rubber (CEC-L-39-T-96),compatibility with acrylic rubber was evaluated in the following manner,A piece of RE2-99 (acrylic rubber) was immersed in the lubricating oilcomposition to be tested at 150° C. for 7 days; and then the degree ofdeterioration of the acrylic rubber piece was evaluated. The results areset forth in Table 1. In Table 1, the pass limits specified in JASO(Japanese Automobile Standard Organization) M355-2005 are also shown.TABLE 1 Comparative Pass Limit Example 1 Example 2 Example A Volume −7to +5 +2 0 +2 change(%) Hardness −5 to +8 +3 +4 +3 change Tensile −15 to+18 +2 +2 −4 strength change (%) Elongation −35 to +10 −23 −19 −35change(%)

The above results shown in Table 1 indicate that both the lubricatingoil compositions of the present invention (Examples 1 and 2) and thatfor Comparative Example A satisfy the JASO standards It is also shownthat the lubricating oil compositions of the present invention wereremarkably improved in the elongation changes as compared with thelubricating oil composition for comparative example.

1. A method of improving the acrylic rubber sealant compatibility in aninternal combustion engine, said method comprising contacting theacrylic rubber sealant in the internal combustion engine and operatingthe internal combustion engine with a lubricating oil compositioncomprising: a) a major amount of a base oil of lubricating viscosity, b)a nitrogen-containing ashless dispersant in an amount of 0.01 to 0.3 wt.% in terms of the nitrogen content, based on the total amount of thelubricating oil composition, c) a metal-containing detergent of analkali metal or alkaline earth metal salt of alkylphenol derivativehaving a Mannich base structure in an amount of 0.001 to 0.04 wt. % interms of the metal content, based on the total amount of the lubricatingoil composition, and d) a phosphorus-containing organic compound in anamount of 0.001 to 0.5 wt. % in terms of the phosphorus content, basedon the total amount of the lubricating oil composition, wherein theratio of components bi) to c) is in the range of from 1:0.005 to 1:2 interms of the nitrogen content.
 2. The method according to claim 1,wherein the nitrogen-containing ashless dispersant is an alkenyl- oralkyl-succinic imide or a derivative thereof.
 3. The method according toclaim 1, wherein the metal-containing detergent of an alkali metal oralkaline earth metal salt of alkylphenol derivative having a Mannichbase structure is represented by the following formula:

wherein R is an alkyl group having 8 to 30 carbon atoms, and n is 0 or apositive integer.
 4. The method according to claim 1, wherein thephosphorus-containing organic compound is selected from the groupconsisting of zinc dihydrocarbyldithiophosphates, zincdihydrocarbylphosphates, phosphoric acid esters, phosphorous acidesters, and thiophosphoric acid esters.
 5. The method according to claim1, wherein the amount of the nitrogen-containing ashless dispersant isin the range of 0.01 to, 0.1 wt. % in terms of the nitrogen content,based on the total amount of the lubricating oil composition.
 6. Themethod according to claim 1, wherein the amount of the metal-containingdetergent of an alkali metal or alkaline earth metal salt of alkylphenolderivative having a Mannich base structure is in the range of 0.002 to0.1 wt. % in terms of the nitrogen content, based on the total amount ofthe lubricating oil composition.
 7. The method according to claim 1,wherein the amount of the phosphorus-containing organic compound is inthe range of 0.01 to 0.2 wt. % in terms of the phosphorus content, basedon the total amount of the lubricating oil composition.
 8. The methodaccording to claim 1, further comprising a metal-containing detergentselected from the group consisting of alkali metal or alkaline earthmetal salicylates, carboxylates, phenates and sulfonates in an amount of1.0 wt. % or less in terms of the metal content, based on the totalamount of the lubricating oil composition.
 9. The method according toclaim 8, wherein the amount of metal-containing detergent selected fromthe, group consisting of alkali metal or alkaline earth metalsalicylates, carboxylates, phenates and sulfonates arid the amount ofthe metal-containing detergent of an alkali metal or alkaline earthmetal salt of alkylphenol derivative having a Mannich base structure isin a ratio of 1:0.003 to 1:1 in terms of the metal content.
 10. Themethod according to claim 1, further comprising a molybdenum compoundselected from the group consisting of an oxymolybdenum complex preparedby the reaction between an acidic molybdenum compound and a basicnitrogen compound, sulfurized oxymolybdenum dithiocarbamate, andsulfurized oxymolybdenum dithiophosphate, in amount of 0.25 wt. % orless in terms of the molybdenum content, based on the total amount ofthe lubricating oil composition.
 11. The method according to claim 1,further comprising an alkali metal borate in an amount of 2 wt. % orless, based on the total amount of the lubricating oil composition. 12.The method according to claim 1, further comprising an oxidationinhibitor selected from the group consisting of hindered phenolcompounds and diarylamine compounds in an amount of 5 wt. % or less,based on the total amount of the lubricating oil composition.
 13. Themethod according to claim 1, wherein the base oil contains 10 wt. % ormore of a mineral oil showing the following characteristics: 17 wt. % orless evaporation loss according to ASTM D-5800 90 wt. % or moresaturated content, 10 wt. % or less, aromatic component, 0.01 wt. % orless, sulfur content, and 120 or more viscosity index.
 14. The methodaccording to claim 1 wherein the lubricating oil composition is a SAEviscosity grade selected from the group 1:5 consisting of 0W20, 0W30,5W20, 5W30 and 10W30.
 15. The method according to claim 14, wherein thelubricating oil composition is a SAE viscosity grade selected from thegroup consisting of 10W30.